You can edit the nginx configuration file (/etc/nginx/conf.d/<YOUR_DOMAIN>/uptime-kuma.conf
) and uncomment these lines :
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
Then check the nginx configuration with nginx -t
and reload nginx if everything is ok : systemctl reload nginx
.
EDIT : Pull request created to fix the app (Fix : Websocket issue after install (see #92) by Gildas-GH · Pull Request #96 · YunoHost-Apps/uptime-kuma_ynh · GitHub)